A proper noun is a noun that refers to a specific, unique entity or place. For example, "London" is a proper noun because it refers to the specific city of London, England. A common noun, on the other hand, is a noun that refers to a general category or type of thing. For example, "theater" is a common noun because it refers to any type of theater.
The phrase "bijou theater" is a common noun because it refers to a general type of theater. A bijou theater is a small, intimate theater that typically seats fewer than 500 people. Bijou theaters are often found in small towns or rural areas, and they often show independent or foreign films.